The present invention relates to a method for making aromatic organic carbonates such as diphenyl carbonate by effecting reaction between an aromatic organic hydroxy compound, such as phenol, and carbon monoxide and oxygen in the presence of an effective amount of a palladium carbonylation catalyst. More particularly, the present invention relates to the carbonylation of an aromatic organic hydroxy compound such as phenol utilizing a mixture of carbon monoxide and oxygen under constant flow conditions to maintain the carbon monoxide and oxygen at a substantially constant molar ratio and partial pressure during the course of the reaction.
Procedures for making diorganic carbonates are shown by Hallgren, U.S. Pat. Nos. 4,361,519 and 4,410,464, utilizing a molecular sieve as a drying agent for the water formed during the reaction and Japanese patent 01,165,551. Aromatic organic carbonates are of particular interest to thermoplastic manufacturers, since they offer an alternative nonphosgene route to aromatic polycarbonates by melt transesterification. A procedure for making aromatic organic carbonates using an organic solvent, such as methylene chloride, is shown by Chalk, U.S. Pat. No. 4,187,242. Reference also is made to T. C. Chang in copending application Ser. No. 217,248, filed Jul. 11, 1988 now abandoned, and EP350-700-A, utilizing a divalent or trivalent manganese salt or cobalt (II) salt and hydroquinone in combination with a palladium catalyst, to catalyze the conversion of an aromatic organic hydroxy compound, such as phenol, to an aromatic organic carbonate. U.S. Pat. No. 4,218,391,Romano et al employ a copper salt to prepare organic esters of carbonic acid. Attempts to use such catalyst with aromatic organic hydroxy compounds, such as phenol, under constant flow conditions have been found to provide unsatisfactory results with respect to % carbonate yields and % carbonate selectivity as compared to the use of aliphatic hydroxy compounds, such as methanol, in preparing aliphatic carbonates under substantially the same conditions.
Aromatic organic carbonates such as diphenyl carbonate made by effecting reaction at elevated pressures in a reactor between components such as, phenol, carbon monoxide, an oxidant and a Group VIII catalyst are generally limited to batch conditions, whereby the pressures of the reacting gases, such as carbon monoxide and oxygen decrease with time and their relative reaction ratio change. Efforts to introduce into the reactor, make-up carbon monoxide and oxygen to improve aromatic organic hydroxy compound conversion, by shutting down the reactor have been unsuccessful because the activity of the Group VIII catalyst is often adversely affected if it is exposed to ambient conditions for even a relatively short period of time.
As a result additional methods are constantly being evaluated to achieve higher reaction rates and aromatic carbonate yields, as well as permitting quantification of reaction rate with respect to gas partial pressure.